1. Field of the Invention
This invention relates to a system for removing particulates from the exhaust gas of internal combustion engines in motor vehicles. More particularly, this invention relates to a system for removing solid, predominately carbonaceous particulates contained in the exhaust gas of diesel engines only during those times that the emission of such particulates into the atmosphere would be of greatest danger to persons in the vicinity of such vehicles.
Diesel engine exhaust gas contains considerable amounts of exhaust particulates. Various kinds of filters or trapping devices have been employed for removing such particulates. However, a typical diesel engine may emit on the order of a gallon of particulate in 1,000 miles of continuous operation After a sufficient amount of particulate has been trapped, the resultant backpressure adversely affects the operation of the engine. Vehicles which utilize filter elements for trapping exhaust particulates must therefore employ means for dealing with this problem.
2. The Prior Art
There have been proposed a number of diesel exhaust gas cleaning devices which include filter regeneration means. Disclosed in U.S. Pat. Nos. 4,450,681, 4,485,621 and 4,538,412 are filter regeneration systems comprising various means for igniting and burning the trapped exhaust particulates. Such regeneration systems conventionally include valve means for by-passing at least a portion of the exhaust gas during at least a portion of the regeneration cycle. In general, regeneration techniques have been subject to one or more of the following disadvantages which have precluded the commercial acceptance thereof: (1) there may be an inability of the filter element to undergo regeneration so as to maintain effectiveness over long periods, (2) regeneration may reduce the efficiency of the filter element, (3) regeneration may damage the filter element such as by the generation of corrosive gases, and (4) regeneration may produce excessive amounts of harmful by-products such as sulfates.